The present invention relates to an automatic document feeder (ADF) for use with an electrophotographic copier, digital copier or similar image recorder for selectively feeding ordinary documents in the form of separate sheets and a continuous document in the form of computer form (CF) paper.
An ADF is extensively used with the above-described kind of image recorder for automatically feeding a document to a glass platen of the image recorder while preventing it from jamming the path or from being damaged, then stopping it on the glass plate, and then discharging it after an image printed thereon has been scanned. Documents usable with the ADF include ordinary documents in the form of separate sheets and elongate documents such as CF paper. Generally, CF paper has a number of sprocket holes formed through a marginal area thereof. Specifically, the sprocket holes are positioned one after another in an intended direction of paper feed to mesh with the teeth of a sprocket which drives the CF paper. A sensor is located on the transport path of the CF paper to sense the sprocket holes. Every time a particular number of sprocket holes associated with one page are sensed, the CF paper is brought to a stop and then copied. An ADF having a capability for transporting such CF paper to the glass platen is disclosed in Japanese Patent Laid-open Publication (Kokai) No. 72455/1984. A drawback with a prior art ADF having such a capability is that once the edge of CF paper where the sprocket holes are positioned is broken or otherwise deformed, the sprocket holes themselves are deformed and cannot be accurately sensed. Then, the amount of transport of the CF paper would deviate from expected one to prevent each image area or print area of the CF paper from being reproduced with accuracy.